1. Field of the Invention
This invention concerns the field of reaction injection molded elastomers using high molecular weight amine terminated polyethers.
2. Description of the Prior Art
In the manufacture of RIM elastomers for use as fascia on automobiles, properties are enhanced by using methylene bis(phenylisocyanate). By using MDI-type isocyanates, elongation and rubberyness are enhanced over the use of higher functionality isocyanates. Since higher functionality isocyanates which improve green strength cannot be used, MDI isocyanates containing a predominance of the 4,4' isomer (usually greater than 90%) are used to enhance the green strength properties.
Therefore, the use of conventional polyols to make RIM elastomers for fascia applications demands the use of an MDI isocyanate containing 90% or more of the 4,4' MDI isomer in order to obtain the acceptable properties of the finished RIM part. In commercially available MDI products the 2,4' isomer has usually been reduced to less than 10% by separation techniques such as distillation. I have discovered a method of making RIM elastomers which allows the use of MDI isocyanates containing less than about 90% 4,4' isomers and, therefore, greater than about 10% 2,4' isomers, but where the properties of the finished RIM part are still excellent. The use of this much less expensive MDI product is of economic benefit.